The present invention concerns a method for moulding a rocker arm for an internal combustion engine, a mould structure for carrying out such a method as well as a rocker arm obtained according to the moulding method.
The invention concerns also a method for machining the rocker arm obtained from the moulding method as well as a rocker arm obtained according to the machining method.
There are known rocker arms of the type comprising a lever body with a first arm co-operating with a cam of a camshaft of the engine and with a second arm co-operating with a valve spindle, the lever body, made of a light metal alloy, being obtained by a chilled diecasting method. The arm which co-operates with the cam comprises an extremely hard reinforcing element which withstands the wear caused by friction with the cam which is inserted during the moulding inside the rocker arm made of light metal alloy. To this end, the reinforcing element is made of sintered material. carbide or special cast iron.
However, the above materials forming the reinforcing element were not always totally satisfying, making therefore the manufacturers use ceramic reinforcing elements presenting a better wear behavior than the above-mentioned metallic materials, provided that the friction surface of the reinforcing element is close to the "mirror polish". The polish of the friction surface of the reinforcing element is obtained according to a known method before the mounting thereof inside the rocker arm which means that the reinforcing element will not be machined after casting or moulding of the rocker arm. All the machining of the rocker arm will therefore be carried out by starting from the reinforcing element.
However, provided that the ceramic reinforcing element is extremely hard and brittle and non-magnetic, it is necessary to maintain it firmly inside the mould without breaking risk.
Moreover, as the blocks obtained after "mirror polish" machining cannot have absolutely identical dimensions, it is necessary to provide a device which permits to compensate for the dimension differences of the blocks.